It is known to operate an LED module including a plurality of light-emitting diodes by means of a single-stage or multi-stage switched mode power supply, which is connected upstream of the LED module. If the LED module has a power range of greater than 25 W, power factor correction (PFC) is additionally required. At low electric powers, a linear regulator is generally used.
Above certain light or power classes, in which, for example, a multiplicity of LEDs are intended to be operated in one module or in a plurality of LED modules, circuit arrangements are known in which many LED chips are connected in series. The forward voltage of this series circuit can in this case be of the order of magnitude of the mains voltage.
In a simple embodiment, series-connected LEDs are operated directly on the AC voltage grid. This results in severe light modulation, so-called “flicker”, and energy-inefficient utilization of the LEDs. For higher power classes, this approach furthermore results in problems associated with normative standards in respect of power factor and harmonics.
Furthermore, it is known to connect a rectifier upstream of the series circuit including LEDs. This is also associated with the abovementioned problems.
In addition, it is known to change the circuitry of the LED series circuit synchronously in time with the mains voltage modulation.
Thus, DE 10 2010 040 266 A1 discloses an LED luminaire including an integrated circuit, a rectifier and a series of series-connected LEDs, which are operated via a rectified AC signal. The integrated circuit has power switches which can short-circuit individually and in a targeted manner a corresponding group of different groups of LEDs in an LED series across which the rectified AC signal is present. If the voltage across the series increases, the integrated circuit controls the power switches in order to increase the number of LEDs through which current flows, while the integrated circuit controls the power switches when the voltage across the sequence decreases in order to reduce the number of LEDs through which current flows.
The document WO 2012/034102A1 describes a system for actuating LEDs directly from a rectified mains voltage with the aid of switches, which bypass groups of LEDs depending on the instantaneous mains voltage.